Fix capitalization for the word "DataLoader" (pytorch#1599)

Change all instances of the word "Dataloader" to "DataLoader" in data_tutorial.py

Co-authored-by: Holly Sweeney <[email protected]>

Author: jangdan

beginner_source/basics/data_tutorial.py

@@ -9,7 +9,7 @@
 `Optimization <optimization_tutorial.html>`_ ||
 `Save & Load Model <saveloadrun_tutorial.html>`_
 
-Datasets & Dataloaders
+Datasets & DataLoaders
 ===================
 
 """
@@ -222,7 +222,7 @@ def __getitem__(self, idx):
 # Iterate through the DataLoader
 # --------------------------
 #
-# We have loaded that dataset into the ``Dataloader`` and can iterate through the dataset as needed.
+# We have loaded that dataset into the ``DataLoader`` and can iterate through the dataset as needed.
 # Each iteration below returns a batch of ``train_features`` and ``train_labels`` (containing ``batch_size=64`` features and labels respectively).
 # Because we specified ``shuffle=True``, after we iterate over all batches the data is shuffled (for finer-grained control over 
 # the data loading order, take a look at `Samplers <https://pytorch.org/docs/stable/data.html#data-loading-order-and-sampler>`_).